1. Field of the Invention
The present invention relates to a printer equipped with a thermal activation device for a heat-sensitive adhesive sheet having a heat-sensitive adhesive layer which is normally non-adhesive and exhibits adhesion only when heated is formed on one side of a sheet-like base material to be used as, for example, an adhesive label. More specifically, the present invention relates to a thermal printer having a thermal head as printing means.
2. Description of the Related Art
Thermal activation sheets (print medium in which a coat layer containing a thermal activation component is formed on the surface, for example, heat-sensitive adhesive sheets) have recently become available as sheets attached to merchandises, and are used in wide fields. Examples of uses of thermal activation sheets include POS sheets for food products, delivery address sheets, sheets bearing medical information, baggage tags, and labels of bottles and cans.
Those heat-sensitive adhesive sheets are composed of a sheet-like base material one side of which has a heat-sensitive adhesive layer and the other side of which is a printable surface. The heat-sensitive adhesive layer is normally non-adhesive and exhibits adhesion when heated.
As a printer for such heat-sensitive adhesive sheets, a printer is proposed which has a thermal activation device which heats a heat-sensitive adhesive layer of a heat-sensitive adhesive label by bringing a head that has resistors (heater elements) on a ceramic substrate as heat sources, e.g., a thermal head for use as a print head in a thermal printer, into contact with the label (JP 11-79152 A).
Now, a description is given on a common structure of a conventional printer for a heat-sensitive adhesive sheet with the use of a thermal printer P shown in FIG. 11.
The thermal printer P in FIG. 11 is composed of: a roll housing unit 10 for holding a tape-like, heat-sensitive adhesive label 70 wound into a roll; a printing unit 50 for printing on the heat-sensitive adhesive label 70; a cutter unit 30 for cutting the heat-sensitive adhesive label 70 into pieces of given length; and a thermal activation unit 60 which serves as a thermal activation device for thermally activating a heat-sensitive adhesive layer of the heat-sensitive adhesive label 70.
The printing unit 50 is composed of: a thermal print head 51 having heater elements which are constituted of relatively small resistors arranged along the width for dot printing; a print platen roller 52 pressed against the thermal print head 51; and other components. In FIG. 11, the print platen roller 52 is rotated clockwise and the heat-sensitive adhesive label 70 is transported to the right hand side of the drawing.
The cutter unit 30 is for cutting the heat-sensitive adhesive label 70 into pieces of suitable length after letters or images are printed on the label by the printing unit 50. The cutter unit 30 is composed of a movable blade 31 operated by a not-shown drive source such as an electric motor, a stationary blade 32 facing the movable blade 31, and other components.
The thermal activation unit 60 is composed of a thermal-activation thermal head 61 having heater elements, a thermal activation platen roller 62 for transporting the heat-sensitive adhesive label 70, and other components. In FIG. 11, the thermal activation platen roller 62 is rotated in a direction opposite the direction in which the print platen roller 52 is rotated (the platen roller 62 is rotated counterclockwise) to transport the heat-sensitive adhesive label 70 to the right hand side of the drawing.
To cut the heat-sensitive adhesive label 70 with the cutter unit 30 in the thermal printer P structured as above, transport of the label 70 has to be stopped for a time period necessary for the movable blade 31 to move up and down (0.4 sec., for example) In other words, the cutter unit 30 cannot perform the cutting operation unless the print platen roller 52 and the thermal activation platen roller 62 stop rotating.
For that reason, in the case where, for example, the label length is longer than the distance between a cutting position of the cutter unit 30 and the thermal-activation thermal head 61, transport of the heat-sensitive adhesive label 70 is stopped with the label 70 nipped between the thermal-activation thermal head 61 and the thermal activation platen roller 62. This causes the heat-sensitive adhesive layer that has exhibited adhesion to stick to the thermal-activation thermal head 61 and prevents smooth transport when the transport of the label is resumed after cutting, leading to transport failures such as paper jam. Another problem is that heat from the thermal-activation thermal head 61 could transfer to the printable layer (heat-sensitive color-developing layer) of the heat-sensitive adhesive label 70 and cause the layer to develop color.
In this case, even if the label is successfully discharged from the printer, the label's appearance has been spoiled and the label is no longer fit for use. If the heat-sensitive adhesive layer is stuck firmly to the thermal-activation thermal head 61, the processing has to be canceled to fix the printer.